Mri-compatible magnet apparatus and associated methods

ABSTRACT

A cochlear implant including a cochlear lead, an antenna, a stimulation processor, and a magnet apparatus, associated with the antenna, including a case defining a central axis, a magnet frame within the case and rotatable about the central axis of the case, and a plurality of elongate diametrically magnetized magnets that are located in the magnet frame, the magnets defining a longitudinal axis and a N-S direction and being freely rotatable about the longitudinal axis relative to the magnet frame.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of, and claims priority to,International Application No. PCT/US2016/056351, filed Oct. 11, 2016,which is a continuation-in-part of, and claims priority to,International Application No. PCT/US2015/066862, filed Dec. 18, 2015,both of which are incorporated herein by reference in their entirety.

BACKGROUND 1. Field

The present disclosure relates generally to the implantable portion ofimplantable cochlear stimulation (or “ICS”) systems.

2. Description of the Related Art

ICS systems are used to help the profoundly deaf perceive a sensation ofsound by directly exciting the intact auditory nerve with controlledimpulses of electrical current. Ambient sound pressure waves are pickedup by an externally worn microphone and converted to electrical signals.The electrical signals, in turn, are processed by a sound processor,converted to a pulse sequence having varying pulse widths, rates, and/oramplitudes, and transmitted to an implanted receiver circuit of the ICSsystem. The implanted receiver circuit is connected to an implantableelectrode array that has been inserted into the cochlea of the innerear, and electrical stimulation current is applied to varying electrodecombinations to create a perception of sound. The electrode array may,alternatively, be directly inserted into the cochlear nerve withoutresiding in the cochlea. A representative ICS system is disclosed inU.S. Pat. No. 5,824,022, which is entitled “Cochlear Stimulation SystemEmploying Behind-The-Ear Sound processor With Remote Control” andincorporated herein by reference in its entirety. Examples ofcommercially available ICS sound processors include, but are not limitedto, the Advanced Bionics Harmony™ BTE sound processor, the AdvancedBionics Naida CI Q Series BTE sound processors and the Advanced BionicsNeptune™ body worn sound processor.

As alluded to above, some ICS systems include an implantable cochlearstimulator (or “cochlear implant”), a sound processor unit (e.g., a bodyworn processor or behind-the-ear processor), and a microphone that ispart of, or is in communication with, the sound processor unit. Thecochlear implant communicates with the sound processor unit and, someICS systems include a headpiece that is in communication with both thesound processor unit and the cochlear implant. The headpiececommunicates with the cochlear implant by way of a transmitter (e.g., anantenna) on the headpiece and a receiver (e.g., an antenna) on theimplant. Optimum communication is achieved when the transmitter and thereceiver are aligned with one another. To that end, the headpiece andthe cochlear implant may include respective positioning magnets that areattracted to one another, and that maintain the position of theheadpiece transmitter over the implant receiver. The implant magnet may,for example, be located within a pocket in the cochlear implant housing.The skin and subcutaneous tissue that separates the headpiece magnet andimplant magnet is sometimes referred to as the “skin flap,” which isfrequently 3 mm to 10 mm thick.

The magnitude of the retention force between the headpiece magnet andimplant magnet is an important aspect of an ICS system. If the force istoo low, the headpiece will not remain in place on the head duringtypical activities. If, on the other hand, the force is too high, thepressure on the skin flap can result is discomfort and tissue necrosis.The magnitude of the retention force is dictated by the strength of themagnets and the distance between the magnets, which is a function of thethickness of the skin flap. The strength of the headpiece magnet isfrequently selected during the post-implantation headpiece fittingprocesses.

The present inventors have determined that conventional cochlearimplants are susceptible to improvement. For example, the magnets inmany conventional cochlear implants are disk-shaped and have north andsouth magnetic dipoles that are aligned in the axial direction of thedisk. Such magnets are not compatible with magnetic resonance imaging(“MRI”) systems. In particular, the cochlear implant 10 illustrated inFIG. 1 includes, among other things, a housing 12 and a disk-shapedsolid block magnet 14. The implant magnet produces a magnetic field M ina direction that is perpendicular to the patient's skin and parallel tothe axis A, and this magnetic field direction is not aligned with, andmay be perpendicular to (as shown), the direction of the MRI magneticfield B. The misalignment of the interacting magnetic fields M and B isproblematic for a number of reasons. The dominant MRI magnetic field B(typically 1.5 Tesla or more) may demagnetize the implant magnet 14 orgenerate a significant amount of torque T on the implant magnet 14. Thetorque T may dislodge the implant magnet 14 from the pocket within thehousing 12, reverse the magnet 14 and/or dislocate the cochlear implant10, all of which may also induce tissue damage. One proposed solutioninvolves surgically removing the implant magnet 14 prior to the MRIprocedure and then surgically replacing the implant magnet thereafter.

One proposed solution involves the use of freely rotatable ball magnetsthat create a magnetic field which can rotate, from the aforementioneddirection that is perpendicular to the patient's skin, to a directionthat is aligned with the direction of the MRI magnetic field B. To thatend, and referring to FIG. 2, one proposed implantable magnet apparatus20 includes a plurality of freely rotatable ball magnets 22 within acase 24. When the magnet apparatus 20 is in very close proximity to anexternal magnet 26, the ball magnets 22 will align with the externalmagnet 26 in the manner shown, with the N-S direction of the ballmagnets being the same as that of the external magnet. When the externalmagnet 26 is removed (FIG. 3), the ball magnets 22 will align with oneanother. The ball magnets 22 will then rotate as necessary in responseto the application of the MRI magnetic field, thereby minimizing thetorque T, because the MRI magnetic field is far stronger than theattraction between the ball magnets. Turning to FIG. 4, the presentinventors have determined that the use of freely rotatable ball magnets22 is less than optimal because the distance between implanted ballmagnets (located within a cochlear implant 28) and the external magnet26 (located within an external headpiece 30) is so great that themagnetic attraction between the ball magnets is greater than themagnetic attraction between the ball magnets and the external magnet.The N-S direction of the ball magnets 22 is perpendicular to the N-Sdirection of the external magnet 26. The increased distance, as comparedto the distance illustrated in FIG. 3, is a product of, for example, thepresence of the implant and headpiece housings and the thickness of theskin flap. The weak magnetic attraction resulting from the misalignmentof the magnetic fields prevents the headpiece from properly mounting tothe patient's head. One possible solution is to simply increase the sizeof the external magnet, thereby increasing the strength of theassociated magnetic field to the point at which the ball magnets 22 in acochlear implant will rotate into the orientation illustrated in FIG. 2.The present inventors have determined, however, that the associatedincrease in the size and weight of the headpiece is undesirable.

Another proposed solution is illustrated in FIG. 5. Here, the cochlearimplant 32 includes a diametrically magnetized disk-shaped magnet 34that is rotatable relative to the remainder of the implant about an axisA, and that has a N-S orientation which is perpendicular to the axis A.The external headpiece 36 includes a diametrically magnetizeddisk-shaped magnet 38 that is not rotatable relative to the remainder ofthe headpiece. The implanted magnet 34 is able to rotate about the axisA into alignment with the external magnet 38, and is also able to rotateabout the axis A into alignment with an MRI magnetic that isperpendicular to the axis A. Turning to FIG. 6, the present inventorshave determined that the use of the diametrically magnetized disk-shapedmagnet 34 is less than optimal because a dominant magnetic field (e.g.,the MRI magnetic field B) that is misaligned by 30° or more maydemagnetize the magnet or generate an amount of torque T on the magnetthat is sufficient to dislodge or reverse the magnet and/or dislocatethe associated cochlear implant.

Another issue is associated with those instances where the user does notprecisely position the headpiece 38 over the cochlear implant 32.Referring to FIG. 5, when the headpiece 36 is precisely positioned overthe cochlear implant 32, the diametrically magnetized implant magnet 34will simply rotate into alignment with the non-rotatable diametricallymagnetized headpiece magnet 38. The magnetic retention force willcorrespond to that selected during the fitting process. In thoseinstances where the headpiece 36 is not precisely placed over theimplant 32, and the implant magnet 34 will rotate into the magneticalignment as shown in FIG. 6A. The magnetic retention force will not,however, be strong enough to pull the headpiece 36 (and its antenna)into alignment over the implant 32 (and its antenna). Moreover, even ifthe headpiece 36 eventually moves to the aligned position over theimplant 32, the electronic lock between the sound processor unit and thecochlear implant will be based on the misaligned position.

SUMMARY

A cochlear implant in accordance with one of the present inventions mayinclude a cochlear lead, an antenna, a stimulation processor, an implantmagnet apparatus, associated with the antenna, including a case defininga central axis, a magnet frame within the case and rotatable about thecentral axis of the case, and a plurality of elongate diametricallymagnetized magnets that are located in the magnet frame, the magnetsdefining a longitudinal axis and a N-S direction and being freelyrotatable about the longitudinal axis relative to the magnet frame. Asystem in accordance with one of the present inventions includes such acochlear implant and an external device. The external device may includean antenna and an external magnet.

There are a number of advantages associated with such apparatus andmethods. For example, a strong magnetic field, such as an MRI magneticfield, will not demagnetize the magnet apparatus. Nor will it generate asignificant amount of torque on the magnet apparatus and associatedcochlear implant. As a result, surgical removal of the cochlear implantmagnet prior to an MRI procedure, and then surgically replacementthereafter, is not required. Moreover, in the absence of the strongmagnetic field, the magnetic attraction between rotatable magnets in themagnet apparatus will not cause the magnets to rotate into anundesirable N-S orientation.

The above described and many other features of the present inventionswill become apparent as the inventions become better understood byreference to the following detailed description when considered inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Detailed descriptions of the exemplary embodiments will be made withreference to the accompanying drawings.

FIG. 1 is a plan view showing a conventional cochlear implant in an MRImagnetic field.

FIG. 2 is a partial section view of a conventional implant magnetapparatus and external magnet.

FIG. 3 is a partial section view of a conventional implant magnetapparatus.

FIG. 4 is a partial section view of a headpiece and an implantedcochlear implant with a conventional implant magnet apparatus.

FIG. 5 is a partial section view of a headpiece and an implantedcochlear implant with a conventional implant magnet apparatus.

FIG. 6 is a partial section view of the implanted cochlear implant witha conventional implant magnet apparatus illustrated in FIG. 5 in an MRImagnetic field.

FIG. 6A is a partial section view of the implanted cochlear implant andheadpiece illustrated in FIG. 5 with the headpiece misaligned.

FIG. 7 is a perspective view of an implant magnet apparatus inaccordance with one embodiment of a present invention.

FIG. 8 is a perspective view of a portion of the implant magnetapparatus illustrated in FIG. 7.

FIG. 9 is a diagrammatic view of a system including the magnet apparatusillustrated in FIG. 7 and a headpiece.

FIG. 9A is a diagrammatic view of a system including the magnetapparatus illustrated in FIG. 7 and a misaligned headpiece.

FIG. 10 is an exploded view of the implant magnet apparatus illustratedin FIG. 7.

FIG. 11 is an end view of a portion of the implant magnet apparatusillustrated in FIG. 7.

FIG. 12 is a perspective view of a portion of the implant magnetapparatus illustrated in FIG. 7.

FIG. 13 is a plan view of a portion of the implant magnet apparatusillustrated in FIG. 7.

FIG. 14 is a section view taken along line 14-14 in FIG. 7.

FIG. 14A is a section view showing a portion of the implant magnetapparatus illustrated in FIG. 14 in a different orientation.

FIG. 15 is a section view similar to FIG. 14 with the implant magnetapparatus in an MRI magnetic field.

FIG. 16 is a perspective view of an implant magnet apparatus inaccordance with one embodiment of a present invention.

FIG. 17 is a section view taken along line 17-17 in FIG. 16.

FIG. 18 is an exploded view of the implant magnet apparatus illustratedin FIG. 16.

FIG. 18A is an enlarged portion of the section view illustrated in FIG.17.

FIG. 18B is an enlarged portion of the section view illustrated in FIG.17.

FIG. 19 is a perspective view of a portion of an implant magnetapparatus.

FIG. 20 is an end view of the portion of an implant magnet apparatusillustrated in FIG. 19.

FIG. 21 is a perspective view of an implant magnet apparatus inaccordance with one embodiment of a present invention.

FIG. 22 is a perspective view of a portion of the implant magnetapparatus illustrated in FIG. 21.

FIG. 23 is a perspective view of a portion of the implant magnetapparatus illustrated in FIG. 21.

FIG. 24 is a plan view of a portion of the implant magnet apparatusillustrated in FIG. 21.

FIG. 25 is a section view taken along line 25-25 in FIG. 21.

FIG. 26 is a perspective view of an implant magnet apparatus inaccordance with one embodiment of a present invention.

FIG. 27 is a perspective view of a portion of the implant magnetapparatus illustrated in FIG. 26.

FIG. 28 is a perspective view of a portion of the implant magnetapparatus illustrated in FIG. 26.

FIG. 29 is a section view taken along line 29-29 in FIG. 26.

FIG. 30 is a perspective view of an implant magnet apparatus inaccordance with one embodiment of a present invention.

FIG. 31 is a perspective view of a portion of the implant magnetapparatus illustrated in FIG. 30.

FIG. 32 is an exploded view of the implant magnet apparatus illustratedin FIG. 30.

FIG. 33 is an end view of a portion of the implant magnet apparatusillustrated in FIG. 30.

FIG. 34 is a top view of a portion of the implant magnet apparatusillustrated in FIG. 30.

FIG. 35 is a section view taken along line 35-35 in FIG. 30.

FIG. 36 is a side view of a portion of the implant magnet apparatusillustrated in FIG. 30.

FIG. 37 is an exploded section view of a portion of the implant magnetapparatus illustrated in FIG. 30.

FIG. 38 is a perspective view of a portion of the implant magnetapparatus illustrated in FIG. 30.

FIG. 39 is a perspective view of a portion of the implant magnetapparatus illustrated in FIG. 30.

FIG. 40 is a perspective view of a portion of the implant magnetapparatus illustrated in FIG. 30.

FIG. 41 is a side view of a portion of the implant magnet apparatusillustrated in FIG. 30.

FIG. 42 is a perspective view of an implant magnet apparatus inaccordance with one embodiment of a present invention.

FIG. 43 is a perspective view of a portion of the implant magnetapparatus illustrated in FIG. 42.

FIG. 44 is a section view taken along line 44-44 in FIG. 42.

FIG. 45 is a section view of an implant magnet apparatus in accordancewith one embodiment of a present invention.

FIG. 46 is a plan view of a cochlear implant in accordance with oneembodiment of a present invention.

FIG. 47 is a block diagram of a cochlear implant system in accordancewith one embodiment of a present invention.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

The following is a detailed description of the best presently knownmodes of carrying out the inventions. This description is not to betaken in a limiting sense, but is made merely for the purpose ofillustrating the general principles of the inventions.

As illustrated for example in FIGS. 7 and 8, an exemplary magnetapparatus 100 includes a case 102, with base 104 and a cover 106, amagnet frame 108, and a plurality of elongate diametrically magnetizedmagnets 110 within the frame that define a N-S direction. The magnetapparatus 100 may, in some instances, be employed a system 50 (FIG. 9)that includes a cochlear implant 200 (described below with reference toFIG. 46) with the magnet apparatus 100 and an external device such as aheadpiece 400 (described below with reference to FIG. 47). The headpiece400 includes, among other things, a housing 402 and a diametricallymagnetized disk-shaped positioning magnet 410 that is not rotatablerelative to the housing.

The exemplary case 102 is disk-shaped and defines a central axis A1,which is also the central axis of the magnet frame 108. The magnet frame108 is freely rotatable relative to the case 102 about the central axisA1 over 360°. The magnets 110 rotate with the magnet frame 108 about thecentral axis A1. Each magnet 110 is also freely rotatable relative tothe magnet frame 108 about its own longitudinal axis A2 (also referredto as “axis A2”) over 360°. As used herein, the phrase “freely rotatableabout an axis” refers to an object that can rotate about an axisrelative to an adjacent object, albeit with some friction between thetwo object, without mechanical limitation of the rotation (e.g., with astop or biasing device that opposes the rotation). In the illustratedimplementation, the longitudinal axes A2 are parallel to one another andare perpendicular to the central axis A1. In other implementations, themagnets within a magnet apparatus may be oriented such that thelongitudinal axes thereof are at least substantially perpendicular tothe central axis A1. As used herein, an axis that is “at leastsubstantially perpendicular to the central axis” includes axes that areperpendicular to the central axis as well as axes that are slightlynon-perpendicular to the central axis (i.e., axes that are offset fromperpendicular by up to 5 degrees). Examples of such magnet apparatus aredescribed below with reference to FIGS. 30-45.

Given the ability of each magnet 110 to freely rotate about itslongitudinal axis A2, the magnets 110 align with one another in the N-Sdirection in the absence of a relatively strong external magnetic field(e.g., the MRI magnetic field discussed above), and the at rest N-Sorientation of the magnets 110 will be perpendicular to the central axisA1, as is illustrated in FIGS. 9 and 14. So oriented, the magneticfields of the diametrically magnetized magnets 110 are aligned with themagnetic field of the diametrically magnetized disk-shaped positioningmagnet 410.

It should also be noted here that the magnetic field of the positioningmagnet 410 is not strong enough to cause the magnets 110 to rotate outof the illustrated at rest N-S orientation. Although the frame 108 willrotate as necessary, the magnets 110 will remain in the N-S orientationillustrated in FIG. 9 and will continue to function as a magnetic unitin the presence of a headpiece magnet. As a result, when the associatedheadpiece is initially misaligned in the manner illustrated in FIG. 9A,the magnetic retention force will be strong enough to pull the headpiece400 (and its antenna) into alignment over the implant 200 (and itsantenna).

The exemplary case 102 is not limited to any particular configuration,size or shape. In the illustrated implementation, the case 102 is atwo-part structure that includes the base 104 and the cover 106 whichare secured to one another in such a manner that a hermetic seal isformed between the cover and the base. Suitable techniques for securingthe cover 106 to the base 104 include, for example, seam welding with alaser welder. With respect to materials, the case 102 (as well as thecases 102 b-102 e described below with reference to FIGS. 21-45) may beformed from biocompatible paramagnetic metals, such as titanium ortitanium alloys, and/or biocompatible non-magnetic plastics such aspolyether ether ketone (PEEK), low-density polyethylene (LDPE),high-density polyethylene (HDPE), ultra-high-molecular-weightpolyethylene (UHMWPE), polytetrafluoroethylene (PTFE) and polyamide. Inparticular, exemplary metals include commercially pure titanium (e.g.,Grade 2) and the titanium alloy Ti-6Al-4V (Grade 5), while exemplarymetal thicknesses may range from 0.20 mm to 0.25 mm. With respect tosize and shape, the case 102 may have an overall size and shape similarto that of conventional cochlear implant magnets so that the magnetapparatus 100 can be substituted for a conventional magnet in anotherwise conventional cochlear implant. In some implementations, thediameter that may range from 9 mm to 16 mm and the thickness may rangefrom 1.5 mm to 3.0 mm. The diameter of the case 102 is 12.9 mm, and thethickness is 2.4 mm, in the illustrated embodiment.

Although the present inventions are not limited to any particularnumber, there are four elongate diametrically magnetized magnets 110 inthe exemplary magnet apparatus 100. Two of the otherwise identicalmagnets 110 are relatively long and two are relatively short in order toefficiently utilize the available volume within the case 102, as is bestshown in FIG. 8. Turning to FIGS. 10-12, the exemplary magnets 110 arenon-circular in a cross-section that is perpendicular to thelongitudinal axis A2 and, in the illustrated implementation, includecurved surfaces 112 and flat surfaces 114. The magnet width W_(M), whichextends in the N-S direction, is greater than the magnet thicknessT_(M), which extends in a direction perpendicular to the N-S direction.The use of elongate diametrically magnetized magnets that are larger inthe N-S direction than in the direction perpendicular thereto reducesthe likelihood of magnet damage, as is discussed in greater detail belowwith reference to FIG. 14. Nevertheless, in other implementations, thecross-sectional shape may be circular. The magnet lengths LM of therelatively long and short magnets 110, i.e. the length in the directionof longitudinal axis A2, are greater than the magnet width W_(M) andmagnet thickness T_(M). Suitable materials for the magnets 110 include,but are not limited to, neodymium-boron-iron and samarium-cobalt.

As illustrated in FIGS. 10 and 13, the exemplary magnet frame 108includes a disk 116 and a plurality of magnet receptacles 118 thatextend completely through the disk and define walls 119 that are locatedbetween adjacent magnets 110. Two of the otherwise identical magnetreceptacles 118 are relatively long and two are relatively short. Themagnet receptacles 118, which are rectangular in shape, have receptaclelengths L_(R) that are substantially equal to (i.e., about 50-100 μmgreater than) the magnet lengths LM, and receptacle widths W_(R) thatare substantially equal to (i.e., about 25-50 μm greater than) themagnet widths W_(M). The receptacle thicknesses T_(R), one the otherhand, are substantially greater than (i.e., about 100-200 μm greaterthan) the magnet thicknesses T_(M). The use of a magnet receptacle thatis thicker than the magnet reduces the likelihood of magnet damage, asis discussed in greater detail below with reference to FIG. 14. In thoseinstances where the apparatus includes magnets with circularcross-sections, similar magnet protection functionality can be achievedby employing a frame that is thicker than the magnet diameter. Suitablematerials for the frame 108 (as well as the frames 108 b-108 e describedbelow with reference to FIGS. 21-45), which may be formed by machiningor injection molding, include paramagnetic metals, polymers and plasticssuch as those discussed above in the context of the case 102.

As illustrated for example in FIG. 14, absent a dominant MRI magneticfield B, the magnets 110 will remain aligned with one another in the N-Sdirection and the N-S orientation of the magnets will be perpendicularto the central axis A1 of the case 102. So oriented, the flat surfaces114 of the magnets 110 will be aligned with one another, will beperpendicular to the central axis A1 and will face the inner surface 120of the case 102. The N-S orientation of the magnets 110 remains thesame, i.e. perpendicular to the central axis A1, both when the externaldiametrically magnetized disk-shaped positioning magnet 410 is present(FIG. 9) and when it is not (FIG. 14).

A gap G, resulting from the difference in receptacle thicknesses T_(R)and magnet thicknesses T_(M), is located between one of the flatsurfaces 114 of each magnet and the inner surface 120 of the case 102that the flat surface faces. The gap G protects the magnets 110,especially those formed from somewhat brittle ceramic materials, fromimpacts to the exterior surface of case 102. For example, when themagnet apparatus 100 is oriented in the manner illustrated in FIG. 14and is impacted by a force F1, the deflection of the case 102 (if any)into the magnet receptacle 118 will not be large enough for the innersurface 120 to impact the adjacent magnet surface 114. If, on the otherhand, a force F2 causes deflection of a portion of the case 102 into themagnet receptacle 118, the magnet 110 will slide into the gap G. In bothinstances, impact on the magnets 100 is minimized. Turning to FIG. 14A,it should be noted that the magnets 110 need not be posited such thatone of the flat surfaces 114 is in contact with an inner surface 120 ofcase 102 to benefit from the gap G. Here, due to the position of themagnet 110, both of the flat surfaces 114 are located adjacent to aportion of the now-split gap G shown in FIG. 14. Accordingly, in thoseinstances where deflection of the case 102 due to force F3 is sufficientto cause the inner surface 120 to come into contact with the adjacentflat surface 114, the magnet 110 can move into the portion of the gapadjacent to the opposite flat surface 114 to prevent magnet damage.

Turning to FIG. 15, when exposed to a dominant MRI magnetic field B, thetorque T on the magnets 110 will rotate the magnets about their axis A2(FIG. 8), thereby aligning the magnetic fields of the magnets 110 withthe MRI magnetic field B. The magnet frame 108 will also rotate aboutaxis A1 as necessary to align the magnetic fields of the magnets 110with the MRI magnetic field B. When the magnet apparatus 100 is removedfrom the MRI magnetic field B, the magnetic attraction between themagnets 110 will cause the magnets to rotate about axis A2 back to theorientation illustrated in FIG. 14, where they are aligned with oneanother in the N-S direction and the N-S orientation of the magnets isperpendicular to the central axis A1 of the case 102.

To facilitate rotation of the magnet frame 108 and/or the magnets 110,lubricious friction reducing material may be provided between the case102 and the magnet frame 108 and/or between the magnets 110 and the case102 and magnet frame 108. For example, the magnet apparatus 100 aillustrated in FIGS. 16-18 is substantially similar to the magnetapparatus 100 and similar elements are represented by similar referencenumerals. Here, however, a pair of lubricious disks 122 and a lubriciousring 124 formed from PTFE, a hard material (e.g. titanium) with alubricious coating, or other suitable materials are positioned betweenthe case 102 and the magnet frame 108. Alternatively, instead of twolubricious disks, a single lubricious disk 122 may be positioned on themagnet frame 108 and the portion of the case 102 that will face theexternal headpiece. In other implementations, a lubricious layer 126 maybe added to the inner surface of the case 102 and/or some or all of thevarious surfaces of the frame 108. The lubricious layer 126 may be inthe form of a specific finish of the inner surface that reducesfriction, as compared to an unfinished surface, or may be a coating of alubricious material such as diamond-like carbon (DLC), titanium nitride(TiN), PTFE, polyethylene glycol (PEG), Parylene, fluorinated ethylenepropylene (FEP) and electroless nickel sold under the tradenames Nedox®and Nedox PF™. The DLC coating, for example, may be only 0.5 to 5microns thick. In those instances where the base 104 and a cover 106 areformed by stamping, the finishing process may occur prior to stamping.Micro-balls, biocompatible oils and lubricating powders may also beadded to the interior of the case 102 to reduce friction.

Alternatively, or in addition, the magnets 110 may be located withintubes 128 formed from low friction material, as is illustrated in FIGS.19 and 20. Suitable materials for the tube 128 include polymers, such assilicone, PEEK and other plastics, PTFE, and PEEK-PTFE blends, andparamagnet metals. The magnets 110 may be secured to the tubes 128 suchthat the each tube rotates with the associated magnet about its axis A2,or the magnets may be free to rotate relative to the tubes. Themagnet/tube combination is also more mechanically robust than a magnetalone. The magnets 110 may, in place of the tube 128, be coated with thelubricious materials discussed above.

Another exemplary magnet apparatus, which is generally represented byreference numeral 100 b in FIGS. 21-25, is substantially similar to themagnet apparatus 100 and similar elements are represented by similarreference numerals. To that end, the magnet apparatus 100 b includes acase 102 b, with a base 104 b and a cover 106 b, a magnet frame 108 b,and a plurality of elongate diametrically magnetized magnets 110 bwithin the frame. The frame 108 b does not include a plurality of magnetreceptacles and walls 119 (FIGS. 10 and 13) that separate adjacentmagnets, as does the frame 108, or any other frame structures thatseparate the magnets. Instead, the frame 108 b includes a disk 116 b anda single magnet receptacle 118 b that extends completely through thedisk. The magnet receptacle 118 b is configured to hold all of themagnets 110 b (four in the illustrated embodiment) and includes arelatively long portion and two relatively short portions. The magnets110 b are elongate diametrically magnetized magnets that are circular incross-section, located within low friction tubes 128, and includerounded corners 111 b. The magnets 110 with flat surface 114 (describedabove with reference to FIGS. 19 and 20) may also be employed.

In the illustrated implementation, the surfaces of the frame 108 b arecoated with a lubricious layer 126 (e.g., DLC), while the inner surfacesof the case 102 do not include a lubricious layer. The very thinlubricious layer 126 reduces friction between the case 102 and frame 108b, while the low friction tubes 128 reduce friction between adjacentmagnets 110 b as well as between the case 102 and the magnets 110 b. Assuch, the aforementioned lubricious disks 122 and a lubricious ring 124may be omitted, thereby reducing the diameter and thickness of themagnet apparatus 100 b as compared to magnet apparatus 100 a (FIGS.16-18). Additionally, although the diameters of the magnets 110 b in theexemplary magnet apparatus 100 b are equal to the widths of the magnets110 (FIG. 11) in the exemplary magnet apparatus 100, the omission of thewalls 119 between the magnets reduces the overall diameter of the magnetapparatus 100 b by an amount ΔD1 (FIG. 25). The diameter of the case 102b is 12.6 mm, and the thickness is 2.9 mm, in the illustratedembodiment.

The overall diameter of the magnet apparatus may be further reduced byreducing the number of magnets in the apparatus while maintaining thesame magnetic strength by including the same total volume of magnetmaterial. To that end, and referring to FIGS. 26-29, the exemplarymagnet apparatus 100 c is substantially similar to magnet apparatus 100b and similar elements are represented by similar reference numbers. Themagnet apparatus 100 c includes a case 102 c, with a base 104 c and acover 106 c, a magnet frame 108 c, and a plurality of elongatediametrically magnetized magnets 110 c within the frame. The frame 108 cincludes a disk 116 c and a single magnet receptacle 118 c, with arelatively long portion and two relatively short portions, which extendscompletely through the disk.

Here, three magnets 110 c with flat portions 114 c are located withinthe magnet receptacle 118 c. Low friction tubes 128 c cover the magnets110 c. The reduction in the number of magnets reduces the overalldiameter of the magnet apparatus 100 s, as compared to the magnetapparatus 100 b, by an amount ΔD2 (FIG. 29). It should be noted that thewidths of the magnets 110 c (FIG. 29) are greater than diameters of themagnets 110 b (FIG. 25) in order to provide the same volume of magneticmaterial, which results in a slight increase in the overall thickness ofthe magnet apparatus 100 c as compared to the magnet apparatus 100 b.The diameter of the case 102 c is 11.6 mm, and the thickness is 3.2 mm,in the illustrated embodiment.

Another exemplary magnet apparatus, which is generally represented byreference numeral 100 d, is illustrated in FIGS. 30-41. Magnet apparatus100 d is substantially similar to the magnet apparatus 100 b and similarelements are represented by similar reference numerals. To that end, themagnet apparatus 100 d includes a case 102 d, with a base 104 d and acover 106 d, a magnet frame 108 d, and a plurality of elongatediametrically magnetized magnets 110 d within the frame. The frame 108 dincludes a disk 116 d and a single magnet receptacle 118 d that extendscompletely through the disk. The magnet receptacle 118 d is configuredto hold all of the magnets 110 d (six in the illustrated embodiment) andincludes a relatively long portion and two relatively short portions.The magnets 110 d are elongate diametrically magnetized magnets that arecircular in cross-section, located within low friction tubes 128 d, andinclude rounded corners 111 d. The magnets 110 with flat surface 114(described above with reference to FIGS. 19 and 20) may also beemployed.

Here, however, at least two of the magnets are slightlynon-perpendicular to the central axis A1 (i.e., have axes that areoffset from perpendicular by any and all angles up to and including 5degrees), as is discussed in greater detail below with reference toFIGS. 35-37. Referring first to FIGS. 30-34, four of the magnets 110 din the illustrated implementation have a longitudinal axis (or “axis”)that is slightly non-perpendicular to the central axis A1 (referred toherein as “slightly non-perpendicular magnets”) and the remaining twomagnets have respective axes that are perpendicular to the central axisA1 (referred to herein as the “perpendicular magnets”). The slightlynon-perpendicular magnets are arranged in two pairs, the magnets in eachpair are positioned end-to-end, and the ends of the magnets in each pairabut one another near the central axis A1.

The north dipoles of the slightly non-perpendicular magnets 110 d in theexemplary magnet apparatus 100 d are aligned with one another withineach pair, as are the south dipoles, so that each pair functions in amanner similar to the longer magnets 110 b of the magnet apparatus 100b. Such N-N and S-S dipole alignment can be problematic during assemblybecause the dipoles repel one another. Connectors 130 d, which arediscussed below with reference to FIGS. 40 and 41, may be provided tomaintain the desired orientation of the magnets 110 d in each pairduring the assembly process. Although the strength of the connectionbetween the magnets 110 d and the connectors 130 d is sufficient tofacilitate assembly, the magnets will rotate about their longitudinalaxis as necessary when exposed to an MRI magnet field. The low frictiontubes 128 d cover less of the connected magnets 110 d due to thepresence of the connector 130 d. Other apparatus and methods foraccommodating dipole alignment during the assembly process are discussedbelow with reference to FIGS. 42-45.

Turning to FIGS. 35-37, the orientation of the slightlynon-perpendicular magnets 110 d may be a function of the shape of thecase 102. In the illustrated implementation, the case base 104 dincludes a convex inner surface 132 d. The central axis A1 passesthrough the apex of the convex inner surface 132 d, and the abuttingends of the slightly non-perpendicular magnets 110 d are adjacent to theapex. The use of the frame 108 d and the shape of the convex innersurface 132 d results in the axes A3 of the slightly non-perpendicularmagnets 110 d being slightly non-perpendicular to the central axis A1(i.e., offset from perpendicular by any non-zero angle Θ up to 5degrees, and by 3 degrees in the illustrated embodiment) and the axes A2of the perpendicular magnets 110 d being perpendicular to the centralaxis A1. These magnet orientations are maintained as the frame 108 drotates relative to the case 102 d and/or as the magnets rotate abouttheir respective axes A2 and A3.

The magnet frame may be configured to accommodate the curvature of theconvex inner surface 132 d of the case base 104 d. To that end, andreferring to FIGS. 38 and 39, the exemplary frame 108 d includes aconcave bottom surface 134 d with a shape corresponding to that of theconvex inner surface 132 d of the case base 104 d. The shape of theframe upper surface 136 d may similarly correspond to that of the innersurface 133 d of the case cover 106 d and, in the illustratedimplementation, both surfaces are flat.

As illustrated for example in FIGS. 40 and 41, the exemplary connectors130 d each include a pair of connector members 138 d that are attachedto one another at an angle (corresponding to the relative orientation ofthe associated slightly non-perpendicular magnets 110 d) with a gap 140therebetween. Each connector member 138 d includes a tubular wall 142 dand an end wall 144 d. The respective sizes of the magnets 110 d and thetubular walls 142 d results in an interference fit that is sufficient tomaintain end-to-end dipole alignment during assembly, but will allow themagnets will rotate about their longitudinal axis relative to theassociated connector 130 d as necessary when exposed to an MRI magnetfield. In some instances, adhesive may be used to secure the ends of themagnets 110 d to the connectors 130 d. The adhesive bonds will fail,thereby permitting magnet rotation, under the torque imparted by an MRImagnet field.

Another exemplary magnet apparatus, which is generally represented byreference numeral 100 e, is illustrated in FIGS. 42-44. Magnet apparatus100 e is substantially similar to the magnet apparatus 100 d and similarelements are represented by similar reference numerals. To that end, themagnet apparatus 100 e includes a case 102 e, with a base 104 e and acover 106 e, a magnet frame 108 e, and a plurality of elongatediametrically magnetized magnets 110 e within the frame. The frame 108 eincludes a disk 116 e and a single magnet receptacle 118 e that extendscompletely through the disk. The magnet receptacle 118 e is configuredto hold all of the magnets 110 e (six in the illustrated embodiment) andincludes a relatively long portion and two relatively short portions.The magnets 110 e are elongate diametrically magnetized magnets that arecircular in cross-section, located within low friction tubes 128 e, andinclude rounded corners 111 e. The magnets 110 with flat surface 114(described above with reference to FIGS. 19 and 20) may also beemployed.

Here, however, the above-described connector 130 d has been omitted, andthere is no other instrumentally connecting the end of the slightlynon-perpendicular magnets 110 e to one another. In some instances, themagnets 110 e may be de-magnetized (or “non-magnetic”) during theassembly process and then magnetized after the magnet apparatus 100 ehas been assembled. It should also be noted here that the magnets in anyof the other embodiments described herein may be magnetized eitherbefore or after assembly.

Turning to FIG. 45, the exemplary magnet apparatus 100 e′ is essentiallyidentical to the magnet apparatus 100 e and similar elements arerepresented by similar reference numerals. Here, however, the ends ofthe slightly non-perpendicular magnets 110 e are secured to one otherwith adhesive 146. The bond formed by the adhesive 146 will maintainend-to-end dipole alignment during assembly, but will fail and allow themagnets 110 e to rotate about their respective longitudinal axes whenexposed to an MRI magnet field.

One example of a cochlear implant (or “implantable cochlear stimulator”)including the present magnet apparatus 100 (or 100 a-100 e′) is thecochlear implant 200 illustrated in FIG. 46. The cochlear implant 200includes a flexible housing 202 formed from a silicone elastomer orother suitable material, a processor assembly 204, a cochlear lead 206,and an antenna 208 that may be used to receive data and power by way ofan external antenna that is associated with, for example, a soundprocessor unit. The cochlear lead 206 may include a flexible body 210,an electrode array 212 at one end of the flexible body, and a pluralityof wires (not shown) that extend through the flexible body from theelectrodes 212 a (e.g., platinum electrodes) in the array 212 to theother end of the flexible body. The magnet apparatus 100 is locatedwithin a region encircled by the antenna 208 (e.g., within an internalpocket 202 a defined by the housing 202) and insures that an externalantenna (discussed below) will be properly positioned relative to theantenna 208. The exemplary processor assembly 204, which is connected tothe electrode array 212 and antenna 208, includes a printed circuitboard 214 with a stimulation processor 214 a that is located within ahermetically sealed case 216. The stimulation processor 214 a convertsthe stimulation data into stimulation signals that stimulate theelectrodes 212 a of the electrode array 212.

Turning to FIG. 47, the exemplary cochlear implant system 60 includesthe cochlear implant 200, a sound processor, such as the illustratedbody worn sound processor 300 or a behind-the-ear sound processor, and aheadpiece 400.

The exemplary body worn sound processor 300 in the exemplary ICS system60 includes a housing 302 in which and/or on which various componentsare supported. Such components may include, but are not limited to,sound processor circuitry 304, a headpiece port 306, an auxiliary deviceport 308 for an auxiliary device such as a mobile phone or a musicplayer, a control panel 310, one or more microphones 312, and a powersupply receptacle 314 for a removable battery or other removable powersupply 316 (e.g., rechargeable and disposable batteries or otherelectrochemical cells). The sound processor circuitry 304 convertselectrical signals from the microphone 312 into stimulation data. Theexemplary headpiece 400 includes a housing 402 and various components,e.g., a RF connector 404, a microphone 406, an antenna (or othertransmitter) 408 and a diametrically magnetized disk-shaped positioningmagnet 410, that are carried by the housing. The headpiece 400 may beconnected to the sound processor headpiece port 306 by a cable 412. Thepositioning magnet 410 is attracted to the magnet apparatus 100 of thecochlear stimulator 200, thereby aligning the antenna 408 with theantenna 208. The stimulation data and, in many instances power, issupplied to the headpiece 400. The headpiece 400 transcutaneouslytransmits the stimulation data, and in many instances power, to thecochlear implant 200 by way of a wireless link between the antennae. Thestimulation processor 214 a converts the stimulation data intostimulation signals that stimulate the electrodes 212 a of the electrodearray 212.

In at least some implementations, the cable 412 will be configured forforward telemetry and power signals at 49 MHz and back telemetry signalsat 10.7 MHz. It should be noted that, in other implementations,communication between a sound processor and a headpiece and/or auxiliarydevice may be accomplished through wireless communication techniques.Additionally, given the presence of the microphone(s) 312 on the soundprocessor 300, the microphone 406 may be also be omitted in someinstances. The functionality of the sound processor 300 and headpiece400 may also be combined into a single head wearable sound processor.Examples of head wearable sound processors are illustrated and describedin U.S. Pat. Nos. 8,811,643 and 8,983,102, which are incorporated hereinby reference in their entirety.

Although the inventions disclosed herein have been described in terms ofthe preferred embodiments above, numerous modifications and/or additionsto the above-described preferred embodiments would be readily apparentto one skilled in the art. The inventions include any combination of theelements from the various species and embodiments disclosed in thespecification that are not already described. It is intended that thescope of the present inventions extend to all such modifications and/oradditions and that the scope of the present inventions is limited solelyby the claims set forth below.

We claim:
 1. A cochlear implant, comprising: a cochlear lead including aplurality of electrodes; an antenna; a stimulation processor operablyconnected to the antenna and to the cochlear lead; and a magnetapparatus, associated with the antenna, including a case defining acentral axis, a magnet frame within the case and rotatable about thecentral axis of the case, and a plurality of elongate diametricallymagnetized magnets that are located in the magnet frame, the magnetsdefining a longitudinal axis and a N-S direction and being freelyrotatable about the longitudinal axis relative to the magnet frame.
 2. Acochlear implant as claimed in claim 1, wherein the magnets each definea N-S rotational orientation; and the magnets are magnetically attractedto one another in such manner that, absent the presence of a dominantmagnetic field, the N-S rotational orientation of the magnets isperpendicular to the central axis of the case.
 3. A cochlear implant asclaimed in claim 1, wherein the magnets each define a length in thedirection of the longitudinal axis, a thickness, and a width; and thelength is greater than the width and the thickness.
 4. A cochlearimplant as claimed in claim 3, wherein the width is greater than thethickness.
 5. A cochlear implant as claimed in claim 4, wherein thewidth extends in the N-S direction.
 6. A cochlear implant as claimed inclaim 3, wherein the magnets each define a cross-section, includingfirst and second curved surfaces that are connected to one another byfirst and second flat surfaces, in a plane perpendicular to thelongitudinal axis; the curved surfaces are separated from one another inthe N-S direction; and the flat surfaces are separated from one anotherin a direction perpendicular to the N-S direction.
 7. A cochlear implantas claimed in claim 3, wherein the magnet frame defines a thickness; andthe thickness of the magnets is less than the thickness of the magnetframe.
 8. A cochlear implant as claimed in claim 7, wherein the magnetframe includes a plurality of magnet recesses, defining recess lengthsand recess widths, in which the plurality of magnets are located; themagnet recess lengths are substantially equal to the magnet lengths; andthe magnet recess widths are substantially equal to the magnet widths.9. A cochlear implant as claimed in claim 3, wherein at least one of themagnets is longer than an adjacent magnet.
 10. A cochlear implant asclaimed in claim 1, wherein the magnets each define a non-circularcross-section in a plane perpendicular to the longitudinal axis.
 11. Acochlear implant as claimed in claim 1, wherein the longitudinal axes ofthe magnets are parallel to one another.
 12. A cochlear implant asclaimed in claim 1, further comprising: lubricious material between thecase and the magnet frame.
 13. A cochlear implant as claimed in claim 1,further comprising: lubricious material between the magnets and themagnet frame.
 14. A cochlear implant as claimed in claim 1, wherein themagnets are located within respective tubes formed from lubriciousmaterial.
 15. A cochlear implant as claimed in claim 1, wherein theantenna, the stimulation processor and the magnet apparatus are locatedwithin a flexible housing.
 16. A cochlear implant as claimed in claim 1,wherein the magnet frame includes a single magnet recesses in which allof the plurality of magnets are located with no portion of the magnetframe located between adjacent magnets.
 17. A cochlear implant asclaimed in claim 16, wherein the single magnet recess includes a firstportion and second and third portions that are shorter than the firstportion.
 18. A cochlear implant as claimed in claim 1, wherein themagnet frame includes a lubricious outer layer.
 19. A cochlear implantas claimed in claim 18, wherein the case defines an inner surface thatdoes not include a lubricious layer.
 20. A cochlear implant as claimedin claim 18, wherein the magnets define respective outer surfaces; andat least a portion of the outer surfaces of the magnets is covered bylubricious material.
 21. A cochlear implant as claimed in claim 1,wherein the longitudinal axes of the magnets are at least substantiallyperpendicular to the central axis.
 22. A cochlear implant as claimed inclaim 21, wherein the longitudinal axis of one or more of the magnets isperpendicular to the central axis; and the longitudinal axis of one ormore of the magnets is not perpendicular to the central axis.
 23. Acochlear implant as claimed in claim 22, wherein two magnets withlongitudinal axes that are not perpendicular to the central axis includelongitudinal ends and are positioned end-to-end with adjacent ends nearthe central axis; and the adjacent ends are connected to one anotherwith a connector that is configured to prevent rotation of the twomagnets about their respective longitudinal axes relative to theconnector in the absence of an MRI magnetic field and to permit rotationof the two magnets about their respective longitudinal axes relative tothe connector in the presence of an MRI magnetic field.
 24. A cochlearimplant as claimed in claim 21, wherein the longitudinal axis of one ormore of the magnets is perpendicular to the central axis; and thelongitudinal axis of one or more of the magnets is offset fromperpendicular to the central axis by 5 degrees or less.
 25. A system,comprising a cochlear implant as claimed in any one of claims 1-24; andan external device including a diametrically magnetized disk-shapedpositioning magnet.
 26. A system as claimed in claim 25, wherein theexternal device includes a housing and the positioning magnet is notrotatable relative to the housing.
 27. A system, comprising a cochlearimplant as claimed in any one of claims 1-24; and a headpiece includingan antenna, and a diametrically magnetized disk-shaped positioningmagnet associated with the antenna.
 28. A system as claimed in claim 27,wherein the headpiece includes a housing and the positioning magnet isnot rotatable relative to the housing.
 29. A method of assembling amagnet apparatus, comprising the steps of: positioning a magnet frameand a plurality of elongate non-magnetic cylinders that each define alongitudinal axis within a case, which includes a base and a cover anddefines a central axis, such that the magnet frame is rotatable aboutthe central axis of the case, the plurality of elongate non-magneticcylinders are within the magnet frame, and each elongate non-magneticcylinder is freely rotatable about its longitudinal axis relative to themagnet frame; securing the cover to the base; and after the cover hasbeen secured to the base, magnetizing the non-magnetic cylinders thatare within the case into diametrically magnetized elongate cylindricalmagnets.